DESCRIPTION (applicant's abstract): Studies of the regulation of morphology and behavior tend to focus on discontinuously variable traits, such as sexual dimorphisms and alternative phenotypes, even though humans and most non-human animals usually express continuous variation in phenotype. Funding for such work usually is based on the assumption that results will apply to continuously variable species that are difficult to study directly. The work proposed here, which aims to understand the role of hormone action in the development of individual variation in behavior, will be one of the first rigorous tests of this assumption. The study will determine whether and how results from discontinuously variable species can be extended to more complex, continuously variable species. The proposed study takes advantage of a recent finding suggesting that neonatal sex steroid hormones control morphological differentiation of the tree lizard, Urosaurus ornatus, a discontinuously variable species. The first aim is to determine the pathway by which sex steroids control morphological differentiation. Based on current evidence, it is predicted that progesterone is the primary regulator. The second aim is to determine whether neonatal progesterone controls behavioral, as well as morphological development. These experiments will establish a solid point-of-comparison for the second half of the study, which will determine whether similar processes regulate the development of discontinuous and continuous behavior variation. The fence lizard, Sceloporus undulatus, will be used to establish whether a) the neonatal hormone profile and b) the behavioral response to early hormone manipulation of a continuously variable species is similar that of a discontinuously variable species. This study will broaden our knowledge of the regulation of continuously variable traits, such as those common in human behavior.